With advance of nanotechnology, the quantum-dot structure has been applied to solar cells to greatly promote the energy conversion efficiency of solar cells.
When a semiconductor material is reduced to quantum dimension, its continuous conduction band gradually splits into narrow energy bands. Thus, electron cooling is slowed down, and the impact ionization effect and Auger recombination effect become obvious. The photoelectric conversion layer is highly associated with the power conversion efficiency of solar cells. Therefore, the application of a quantum-dot structure to the photoelectric conversion layer favors collecting effective carriers in the photoelectric conversion layer and thus promotes the power conversion efficiency of solar cells.
A US publication No. US2010/0288345 disclosed a quantum-dot thin-film solar cell, which comprises a substrate, a first electrode layer, an active layer, and a second electrode layer. The first electrode layer is arranged on the substrate, and the second electrode layer is arranged over the first electrode layer. The active layer is arranged between the first and second electrode layers, and two sides thereof respectively contact the first and second electrode layers. A plurality of quantum dots is formed inside the active layer to increase the power conversion efficiency of the solar cell.
The quantum dots can indeed increase the range of the absorbable wavelengths of the incident light. However, they can only increase the power conversion efficiency to a limited extent because of reflection of incident light and insufficient diffusion distance of carriers. Therefore, the conventional technology still has room to improve.